Japanese Patent Laid-Open Publication Nos. 2005-196860, 2002-288846, and 2005-122792 disclose methods of cooling the pickup of a conventional optical disc drive for a personal computer or an optical disc recorder/player by improving the structure of the pickup or a structure in the recorder/player. The pickup is liable to be hot because it has a laser diode, which is one of heat sources. In the optical disc drive disclosed in Japanese Patent Laid-Open Publication No. 2005-196860, the heat source of the pickup is connected with low thermal resistance through a member of high thermal conductance to a cooling fin, which is fitted in a portion of the recorder/player that is exposed to the air flow formed by disc rotation. In the optical disc drive disclosed in Japanese Patent Laid-Open Publication No. 2002-288846, the main heat source of the pickup is positioned near the guiding shaft of the mechanism for moving the pickup. This optical disc drive has another bearing for heat transfer from the pickup to the guiding shaft in addition to the bearing for the movement. The main heat source of this pickup is connected with low thermal resistance to the guiding shaft. The optical disc drive disclosed in Japanese Patent Laid-Open Publication No. 2005-122792 has a non-contacting cooling plate facing the bottom of the pickup and positioned near it and within the range which the pickup moves. The heat source of this pickup is connected to the cooling plate with low thermal resistance through the air layer in the narrow clearance between this plate and the pickup bottom.
In Japanese Patent Laid-Open Publication No. 2005-196860, the replacement of graphite or another special material with a general metallic material or another method makes it possible to further increase the originally good heat radiation caused by convection at the upper side (limited to the center, which is not covered by a cover), front side, and back side of the pickup, which are exposed to the air flow formed by disc rotation. However, at many other portions such as the under, right, and left sides of the pickup, the air flow and convection are weak, so that the amount of heat radiation is small. This prevents the whole pickup from being cooled sufficiently. In Japanese Patent Laid-Open Publication No. 2002-288846, it is possible to reduce the thermal resistance from the pickup to the guiding shafts. However, the diameters, thermal conductances, surface areas, etc. of the guiding shafts are limited, so that high thermal resistance is created by the thermal conduction and convection to the parts etc. to which the guiding shafts are fixed and the ambient air. This limits the increase in the heat radiation through the guiding shafts, so that the whole pickup cannot be cooled sufficiently. In Japanese Patent Laid-Open Publication No. 2005-122792, the heat radiation from the under side of the pickup can be increased by the convection and radiation from the cooling plate, which is large in area, to the ambient air etc., with the under side of the pickup and the cooling plate positioned very close to each other (about 0.3 mm) so that the thermal resistance created by the thermal conduction and radiation through the air layer can be low. This may make it possible to cool the whole pickup well in addition to the heat radiation from the upper, front, and back sides of the pickup, which is even normally good as stated above. However, if the clearance between the under side of the pickup and the cooling plate is narrowed merely to the foregoing extent, the pickup and the cooling plate are liable to come into contact with each other due to deformation etc. of the parts connected to them. The contact between the pickup and the cooling plate increases the moving resistance to the pickup and causes needless electric conduction to the pickup, so that normal recording on and normal reproduction from a disc become difficult. This publication also discloses a method for radiating more heat by filling the clearance with heat-conducting grease, which interferes with the movement of the pickup remarkably, contaminates the optical parts remarkably, and causes other operational problems. The cooling plate is well known and basically identical in structure with the under cover protecting the under side of main parts in the housing of a slim tray-type optical disc drive in which the main parts protrude from the housing when a disc is mounted or dismounted.
The object of the present invention is to provide a method for sufficiently cooling the pickup, which becomes hot in particular, of an optical disc drive without causing problems to the operation of the drive.